The present invention relates to a golf ball molding die and a golf ball manufactured by using the die. More particularly, it relates to an improvement of a die used for molding a golf ball.
A golf ball is usually manufactured by an injection molding process or a compression molding process. In the case of an injection molding process, an injection molding die is used. In this injection molding die, a spherical cavity is formed.
When a golf ball is molded, air that is present in a gap between the wall surface of the cavity and a rubber elastic body, which is the core material for the golf ball, and a volatile constituent such as a gas released mixedly with a resin are discharged to the outside of the die through a gap between a support pin for supporting the golf ball in the cavity and a support pin accommodating hole.
If the air and the volatile constituent such as a gas are not discharged well, what is called a weld-mark such as a bird footprint is formed on the surface of the golf ball (weld defect). Further, in some cases, a defect called “burning” may be produced by adiabatic compression of gas in the cavity. To prevent such defects, a large venting hole is conventionally provided to dissipate the gas. In this case, however, the clearance between the pin and the hole must be made large, which results in the production of relatively large burrs on the surface of the golf ball. As a result, a full-scale burr treatment process must be introduced, so that there arises a problem of significantly increased manufacturing cost.
As another method for dissipating the gas, Japanese Unexamined Patent Application Publication No. 2004-215684 has proposed a technique in which a plurality of convex parts and concave parts are formed alternately in the circumferential direction on the side surface of the support pin. Thereby, the clearance between the concave part and the accommodating hole is increased. However, this support pin has a problem of being easily broken as compared with the case where the convex parts and concave parts are absent.